Amphoteric surfactants and copolymerizable amphorteric surfactants for use in latex paint

ABSTRACT

Amphoteric surfactants and copolymerizable amphoteric surfactants for use in latex paints are presented. These surfactants, which contain positively charged nitrogen, are incorporated into the paint formulations at low levels and impart superior wet adhesion and freeze-thaw stability.

This application is a division of U.S. Ser. No. 07/537,711 filed Jun.13, 1990 now U.S. Pat. No. 5,064,888.

BACKGROUND OF INVENTION

Latex-based paints have captured a significant portion of both theindoor and outdoor paint markets due to a number of significantadvantages these paints possess over the solvent-based paint products.The primary advantages are low odor, easy clean-up, and fast dry,however, the paints suffer from the drawback of poor "wet adhesion".

Latex-based paints generally comprise three components, an emulsionpolymer or copolymer which is film forming (the latex), an aqueous phase(which contains, inter alia, additives such as pigments, defoamers andantifreeze agents) and one or more surfactants. Various additives areoften contained in the formation as particular applications dictate.

Two types of emulsion polymers are generally used in formulating latexpaints. The first type comprises copolymers of alkyl esters of acrylicand methacrylic acid with minor amounts of acrylic and methacrylic acidand are termed "all acrylic". All acrylic paints produce hard coatingswhich are resistant to scrubbing and provide good water resistance andwet adhesion. However, because of the cost of the acrylic monomers allacrylic paints are mainly used in premium or high quality paints.

The second type of latex comprises vinyl acetate terpolymers incombination with softer acrylic monomers. This type of latex, oftencalled "vinyl acrylic", are cheaper than the all acrylics. The paintsproduce films which are hard, but tend to have a much lower wet adhesionthan their acrylic based counterparts.

The term "wet adhesion" is used in the paint industry to describe theability of a paint to retain its adhesive bond (to the substrate) underwet (or high humidity) conditions. Organic solvent-based paintsgenerally exhibit good wet-adhesion but water-based (latex) paints oftentend to exhibit reduced wet-adhesion under wet or humid conditions. Thisinherent deficiency severly limits the utility of latex paints in areaswhere humid environments might be encountered, e.g. exteriors, bathroomsand kitchens. Further, painted surfaces which become soiled must bewashed and cleaned, often using water and abrasive scrubbing compounds.Because of their tendency to have lower wet-adhesion, the latex paintsare also much less scrub-resistant than their organic solvent basedcounterparts.

Much effort has been devoted in recent years to improving the wetadhesion of latex-based paints. Some researchers have attempted to varyvarious paint formulation component parameters, such as pigment types,dispersant types, and coalescing agents to improve wet adhesion; howeverthe most significant improvements in wet adhesion properties has beenobtained by the functional modification of the copolymeric backbone ofthe latex. Specifically, incorporation of amine, amide, and acetoacetatefunctionalities into the copolymer have shown promising results. Forexample, cyclic ureido derivatives have been described in the patentliterature as imparting wet adhesion properties, e.g. U.S. Pat. Nos.4,104,220, 4,111,877, 4,219,454, 4,319,032 and 4,599,417.

These compounds are described as improving wet adhesion properties forvinyl acetate terpolymers when copolymerized with them. However, wetadhesion monomers are very expensive and their inclusion results in adrastic increase in the cost of the vinyl acetate terpolymers andall-acrylic copolymers used in the paint.

A further problem observed with latex paints is that of destabilizationdue to freezing and thawing. During freeze-thaw cycling, the anionicsurfactants commonly employed in latex paints tend to desorp from thelatex particles, thereby increasing the ionic strength of the aqueousphase, ultimately resulting in paint coagulation due to destabilizationof the electronic double layer surrounding each particle. Thus, theviscosity of the paint will vary as more freeze/thaw cycles areencountered. Ordinarily, antifreeze compounds (e.g. ethylene glycol) areadded to the paints to combat this, but this contributes to the cost ofthe paint and also requires the use of volatile organic compounds.

Researchers have attempted to alleviate this problem by using blends ofsurfactants in place of the anionic surfactant. For example, U.S. Pat.No. 3,193,517 discloses a method for making a viscosity-stable latex byblending a cationic surfactant, an amphoteric surfactant, and a nonionicsurfactant in a prescribed ratio. However, the blended system is notentirely satisfactory in many other respects.

There exists a real need for both wet-adhesion promoters and viscositystabilizers for use in latex paints.

The onset of paint coagulation can therefore be delayed or eliminatedentirely.

The amphoteric surfactants of this invention can thus be used to producelatex paints having wet adhesion values in the range of the alkyds, evenwhen vinyl acrylics are used in the paint, which also are more stabletoward freeze/thaw cycling than conventional latex paints.

DETAILED DESCRIPTION OF INVENTION

The amphoteric surfactants of this invention comprises three main types:

1. SO₃ ⁻ containing surfactants of the formula ##STR1## wherein R₁ =C₈-C₂₀ alkyl, preferably C₈ -C₁₂ alkyl

R₂ =H or C₁ -C₂ alkyl, preferably methyl

n=2-6, preferably 2

2. COO⁻ containing surfactants of the formula ##STR2## wherein R₁ =C₈-C₂₀ alkyl, preferably C₈ -C₁₂ alkyl

R₂ =H or C₁ -C₂ alkyl, preferably methyl

n=1-4, preferably 1

3. Copolymerizable amphoteric surfactants of the formula ##STR3##wherein R₁ =C₁ -C₂ alkyl

R₂ =C₁ -C₂ alkyl

X⁻ =SO₃ ⁻ -- or COO⁻

a=2-3

b=1-6

The first two types are surfactants which are used in the latexpreparations at a concentration of 1-4 pphm (parts per hundred monomer,by weight) and yield superior wet adhesion.

The third type is a copolymerizable amphoteric surfactant which isactually copolymerized into the polymeric backbone of the latexcopolymer. The surfactant is incorporated at a rate of 1-3 pphm.

While the above amphoteric surfactants may be utilized as the only wetadhesion monomer/surfactant in the paint formulation, it has been foundthat inclusion of small amounts of non-ionic surfactants of the generalformula ##STR4## wherein R=C₄ -C₁₂ alkylphenol or C₄ -C₁₈ alkyl,preferably C₈ -C₉ alkylphenol or C₁₂ -C₁₅ alkyl and n is about 20-50 inthe formulation serves to stabilize the latex emulsion and enhancemechanical stability.

The nonionic surfactants are preferably incorporated at a level of 1-3,preferably 2.5 pphm when the blended surfactants are used, and 0.5-0.7pphm when the copolymerizable amphoteric surfactants are used.

The above amphoteric surfactants can be used with virtually any latexpaint system including vinyl acrylic and all acrylic systems. Thesurfactants improve the wet adhesion of the paints, especially the vinylacrylics, and stabilize the paints toward freeze-thaw cycling. Thissecond property is particularly advantageous as it permits the reductionor elimination of the antifreeze agent, typically ethylene glycol, inthe paint. Ordinarily paint formulations contain significant amounts ofantifreeze (5-10% by wt or more). As environmental concerns areincreasing, the demand for paints with low or no volatile organiccompounds (VOC) paints is increasing. The use of these surfactants willaid in this reduction, permitting low (<2% by wt) or no VOC formulationsto be prepared.

EXAMPLES

The following examples illustrate certain preferred embodiments of theinvention, but are not intended to be illustrative of all embodiments.

Example I--Production of a MMA/BA latex

This example illustrates the preparation of an all-acrylic (methylmethacrylate butyl acrylate) latex containing a standard wet adhesionmonomer Sipomer® WAM (a product of Alcolac Ltd.) using an anionicsurfactant sodium lauryl sulfate (Sipex® UB of Alcolac, Ltd.).

Briefly, a 12-liter stainless steel reactor, the primary vessel, wascharged with the following:

    ______________________________________                                                               Concentration                                          Compound       Grams   in PPHM.sup.1                                          ______________________________________                                        H.sub.2 O      1991    59.17                                                  ______________________________________                                        A monomer pre-emulsion was formed in secondary vessel I                       comprising:                                                                   Secondary Vessel I                                                                                       Concentration                                      Compound           Grams   in PPHM.sup.1                                      ______________________________________                                        Butyl Acrylate (BA)                                                                              1742    51.8                                               Methyl Methacrylate (MMA)                                                                        1623    48.23                                              Water               654    19.43                                              Sipex UB (27%)      182     5.40                                                                         (1.5 part solids)                                  Rexol 25/407 (70%)  88      2.61                                              ______________________________________                                    

Three other secondary vessels were charged as follows:

    ______________________________________                                                                 Concentration                                        Compound         Grams   in PPHM.sup.1                                        ______________________________________                                        Secondary Vessel II                                                           Ammonium Persulfate                                                                            14.0    0.42                                                 H.sub.2 O        250     7.43                                                 Secondary Vessel III                                                          H.sub.2 O        100.0   2.97                                                 Sipomer WAM      38.0    1.13                                                 Secondary Vessel IV                                                           H.sub.2 O        300     0.9                                                  SMBS             10      0.3                                                  ______________________________________                                         Notes:                                                                        .sup.1 based on the final formulation                                    

Initially, mild agitation was affected in the primary vessel and thereaction content was heated to 55° C. Subsequently added were 164 gm ofpre-emulsion Secondary Vessel I) 24 gm of A.P. solution (SecondaryVessel II), and 29 gm of SMBS solution (Secondary Vessel IV). Afterincubation of the mixture for 10 minutes the remaining contents ofsecondary vessels I, II, III, and IV were added and the pH of theresultant emulsion was then adjusted to 8 by the addition of 26.6%aqueous ammonium hydroxide solution.

The particle size of the latex was determined by a BI-90 particle sizeanalyzer (Brookhaven Instruments). The resultant latex (Acrylic A) had asolid content of 50%, the average particle size diameter was 164 nm andthe viscosity was 90 cps.

A second latex (B) was prepared according to the above procedure, exceptthat Siponate DS-10 (sodium dodecyl benzene sulfonate) at 1.6 pphm wassubstituted for the Sipex® UB (sodium lauryl sulfate) in secondaryvessel I. The resulting latex (Acrylic B) had a solid content of 50percent and an average particle size of 150 nm.

A third emulsion analogous to Acrylic B was made except no Sipomer WAMwas introduced in secondary vessel III, and was identified as Acrylic C.The resulting emulsion had solid content of 50% and an average particlesize of 174 nm.

Example II--Preparation of all acrylic Latexes

Two all acrylic latexes were synthesized each employing amphotericsurfactants of this invention namelyN,N-Dimethyl-N-lauryl-N-(3-Sulfopropyl) ammonium-betaine (Hartomer HB5175 of Hart Chemical Ltd.), and Cocoammonium betaine (Hartomer HB6300).

The acrylic latexes, identified as D and E, were prepared essentiallyfollowing the procedure in Example I wherein 1.6 parts per hundredmonomer of amphoteric surfactants namely Hartomer HB-5175 and, HartomerHB-6300 respectively, were used instead of Sipex UB. The followingproperties were observed:

    ______________________________________                                                        Latex                                                                         D     E                                                       ______________________________________                                        particle size (nm)                                                                              360     310                                                 viscosity (cps)   25      27                                                  % solids          49.9    49.9                                                ______________________________________                                    

Example III--Preparation of Latex Paint Formulations

To assess the utility of the above latexes in paint, the following paintformulations was prepared by mixing the following ingredients:

    ______________________________________                                        Semi Gloss Paint Screening Formula I                                          Compounds              Grams                                                  ______________________________________                                        Ethylene Glycol        81                                                     Colloid 226-35 (1)     7.5                                                    Drew L-475 (2)         3.0                                                    Water                  30                                                     Titanox 2020 (3)       300                                                    Snowhite 10-1 (4)      50                                                     Disperse to 5-6 Hegman (5) and add:                                           Water                  265                                                    Methocel J5MS (6)      2                                                      Latex                  530                                                    Rexol 25/9 (7)         4.0                                                    Texanol (8)            l0.0                                                   AMP-95 (9)             3.0                                                    UCAR SCT-275 (10)      25.0                                                   Kathon LX (11)         3.0                                                    Drew L-475 (2)         6.0                                                    ______________________________________                                         Notes:                                                                        (1) A non foaming, water soluble anionic dispersant containing 35% of         active, and having a pH of 7.5 and specific gravity of 1.23.                  (2) A defoamer prepared from a blend of mineral oils and silica               derivatives containing 100% of active material.                               (3) Rutile titanium dixoide, also known as Tioxide HD6X.                      (4) Calcium carbonate having the properties:                             

    CaCO.sub.3     92.5%                                                          dry brightness 95.5                                                           specific gravity                                                                              2.65                                                          less than 10 microns                                                                         90%                                                            mean particle size                                                                            3 microns                                                     Hegman grind    6.5                                                           oil absorption 16                                                              (5) A grind measurement used by the paint industry.                           (6) Hydroxy propyl cellulose.                                                 (7) An ethoxylated nonyl phenol surfactant (nonionic) containing 9 to 10      moles of ethylene oxide.                                                      (8) 2,2, 4Trimethylpentanediol-1,3, monoisobutyrate and used as coalescin     agent.                                                                        (9) 2amino-2-methyl-1-propanol.                                               (10) A nonionic watersoluble polyetherpolyurethane thickener.                 (11) A microbiocide having, as active ingredients,                            5chlor-2-methyl-4-isothiazolin-3-one and 2methyl-4-isothiazolin-3-one and     containing 14% active ingredients.                                       

The ingredients were mixed for 15 minutes, after which the formulationwas ready for use.

A second paint formulation, SEMI-GLOSS PAINT SCREENING FORMULA (II), wasprepared following the recipe in SEMI-GLOSS PAINT SCREENING FORMULA (I)except 20 gram of ethylene glycol was used instead of 81 gm of ethyleneglycol.

Example IV--Freeze-Thaw Stability

The paint compositions made employing acrylic latexes A-E were testedfor freeze-thaw stability in semi-gloss paint screening formula (I).Briefly, the paint formulations were subjected to repeated freeze-thawcycling by chilling to -18° C. for 16 hours subsequently warming to roomtemperature for 8 hours. The test was continued until the latexcoagulated, or to a maximum of five (5) cycles. The results arepresented below:

    ______________________________________                                        Latex                                                                         A            B        C.sup.b  D      E                                       Surfactants:                                                                          Concentration (pphm)                                                  ______________________________________                                        Sipex UB                                                                              1.5      X        X      X      X                                     Siponate                                                                              X        1.6      1.6    X      X                                     DS-10                                                                         Hartomer                                                                              X        X        X      1.6    X                                     HB-575                                                                        Hartomer                                                                              X        X        X      X      1.6                                   HB-6300                                                                       Freeze-thaw                                                                   (No. of 1        1        1      5      5                                     Cycles)                                                                       OBSER-  COAG-    COAG-    COAG-  LIQUID LIQUID                                VATION  ULATE    ULATE    ULATE                                               ______________________________________                                         a. In parts per hundred monomer                                               b. No wet adhesion monomer on polymer backbone                           

Formulations A-C employing standard anionic surfactants coagulated aftera single cycle, while D and E, which employed the amphoteric surfactantsof this invention were stable (still liquid) after 5 cycles.

Example V--Scrub Resistance

A sixth acrylic latex, identified as Latex F was synthesized using theprocedure shown in Example I. The following monomer and surfactantcomposition (in pphm) were used:

    ______________________________________                                        Butyl acrylate (BA)  52.0                                                     Methyl methacrylate (MMA)                                                                          48.0                                                     Methacrylic acid (MAA)                                                                             1.2                                                      Sipomer WAM          1.0                                                      Sipex UB             1.0                                                      Rexol 25/407         4.3                                                      Product Properties:                                                           % Solids, 50; particle size (nm) 105;                                         Grits (200M) .001.                                                            ______________________________________                                    

Another all acrylic latex, G, was synthesized following analogousprocedure to acrylic resin F except Hartomer MB-5175 was substituted forSipex UB. Latexes F and G were respectively tested for freeze-thaw andwet adhesion in semi-gloss paint screening formula (I).

both of these latexes differed from the latexes of Example I as follows:

1. MAA was introduced on the polymer backbone;

2. The anionic surfactant level was lowered;

3. The noionic surfactant level was increased.

These latexes were subjected to a standard wet adhesion test procedure,as follows: Briefly, a leneta scrub panel was prepared by making adrawdown of a standard semi-gloss alkyd base (this base was chosen asbeing the most difficult test for wet adhesion), using a 3-mil base. Thepanels were then aged at least a week at room temperature.

Subsequently, the test latex was drawn down on aged alkyd surface usinga 3-mil bird applicator and allowed to dry for 48 hours. The followingabrasive scrub resistance test procedure then was followed:

1. The test chart was affixed to a glass panel and put into the scrubmachine;

2. The test brush was immersed in warm water for 30 minutes to conditionbefore tests;

3. Ten (10) separate containers 8 gms. each of Ajax (abrasive cleanser)were weighed out;

4. The test brush was placed in the holder and then put over top of thetest chart, 200 gm of warm water were then added;

5. The scrub machine was then started and run for 400 strokes;

6. If the coating remained intact, 8 gm dry Ajax were then placed underthe brush, and the machine was run 100 strokes.

7. Step 6 was repeated until coating failure, i.e., when paint stripsfrom the alkyd.

The number of brush scrubs to achieve failure is recorded.

The results are presented below:

    ______________________________________                                                    Acrylic Resin F                                                                         Acrylic Resin G                                         ______________________________________                                        Wet Adhesion  1100        1743                                                (Scrubs to failure)                                                           Freeze-thaw     3           5                                                 (no of cycles stable)                                                         Observation   4th cycle   liquid                                                            coagulation                                                     ______________________________________                                    

The above example demonstrates that amphoteric surfactants of thisinvention, even when used together with wet adhesion monomer SipomerWAM, enhances the wet adhesion capabilities of the acrylic latex.

Example VI--Freeze-Thaw Stability, Low Ethylene Glycol Formulations

Latexes A and D were tested in SEMI-GLOSS PAINT SCREENING FORMULA (II)wherein the amount of ethylene glycol (anti-freezing compound) waslowered to one fourth the level as compared to ethylene glycol informula I.

    ______________________________________                                                     Acrylic Resin                                                                 D          A                                                     ______________________________________                                        Ethylene Glycol (%)                                                                          1.5          6.14                                              Freeze-thaw    PASS         FAIL                                                             (remained liquid                                                                           (coagulated                                                      for five cycles)                                                                           after 1 cycle)                                    ______________________________________                                    

This example shows that latex synthesized employing amphotericsurfactants imparts freeze-thaw stability in the paint composition. Theamount of ethylene glycol can, thus, be significantly lowered as shownin the above example.

Example VII--Electrolyte Tolerance

An acrylic latex, H, was synthesized using amphoteric surfactantHartomer HB-5175 following the procedure for resin D, except that 7.8pphm CaCl₂ was added to the initial charge and no Sipomer WAM was used.The resultant formulation had the following physical properties: %Solids 52.0; particle size (nm) 484; grits (100M) 0.0016.

An attempt to synthesize a latex using an anionic surfactant (Sipex UB)in the presence of 2.5 pphm of CaCl₂ was unsuccesful due to coagulationof the formulation.

Thus, latexes made using the amphoteric surfactants of the invention aremore tolerant to electrolytes as compared to those made with anionicsurfactants.

Example VIII--Vinyl Acrylic Latexes

A vinyl-acrylic emulsion, made with anionic and nonionic surfactants andcontaining no wet adhesion monomer was obtained commercially. Theproduct characteristics are listed below:

    ______________________________________                                        Latex I                                                                       ______________________________________                                        % Solids        55.0                                                          Viscosity (cps) 1000-2000                                                     pH              5-6                                                           Particle size   350-450 nm                                                    ______________________________________                                    

Example IX--Wet Adhesion of Vinyl Acrylic Latexes

A vinyl acetate copolymer having the same basic formula as Latex I, wassynthesized by substituting 1 pphm of amphoteric surfactant HartomerHB-5175 for the anionic surfactant. This was identified as Latex J.

Both latexes were incorporated in SEMI-GLOSS PAINT SCREENING FORMULATIONI, and the resultant formulations were examined for scrub resistance(wet adhesion) following the procedure of Example V. The results aresummarized below:

    ______________________________________                                                         Latex                                                                         I   J                                                        ______________________________________                                        Wet Adhesion       92    480                                                  (scrubs to failure)                                                           ______________________________________                                    

Thus, the wet adhesion capabilities of vinyl acrylic latex paints can begreatly improved by using amphoteric surfactant instead of anionicsurfactants.

Example X--Preparation of Latexes with Copolymerizable AmphotericSurfactants

An all acrylic latex polymer, identified as Latex K was synthesizedusing an amphoteric copolymerizable surfactant of this invention, namelyN(3-Sulfopropyl)-N-methacryloxyethyl-N, N-dimethyl ammonium betaine(Hartomer HB-6380, Hart Chemical, Ltd.). The following monomer andsurfactant compositions in parts per hundred monomer (pphm) were used tosynthesize the acrylic latex:

    ______________________________________                                               BA       5.05                                                                 MMA      48.5                                                                 AA       1.0                                                                  HB-6380  2.2                                                                  Rexol 25/40                                                                            0.6                                                           ______________________________________                                    

The following properties were observed:

    ______________________________________                                        Particle size (nm)                                                                             540                                                          Viscosity (cps)  34.0;                                                        pH               7.0                                                          % solids         51.06                                                        ______________________________________                                    

A second latex, identified as Latex L, was made employing anionicsurfactant Siponate DS-10 instead of the amphoteric surfactant. Latex Kand L were tested for freeze thaw stability in SEMI-GLOSS PAINTSCREENING FORMULATION I, except that no ethylene glycol was added.

    ______________________________________                                                   Emulsion                                                                      K         L                                                        ______________________________________                                        freeze-thaw  5           --                                                   (no of cycles)                                                                             (still liquid after                                                                       (coagulated                                                       5 cycles)   after 1 cycle)                                       ______________________________________                                    

Thus, the paint formulation containing copolymerizable amphotericsurfactant exhibited a good freeze-thaw stability, even without ethyleneglycol.

Example XI--Freeze-Thaw Stability

An all acrylic latex of this invention, identified as Latex M wassynthesized using an amphoteric copolymerizable surfactant namelyN-(aceto) -N-methacryloxyethyl-N,N-dimethyl ammonium betaine (HartomerHB-6420, Hart Chemical, Ltd.) as in Example X. The resultant latex hadthe following physical properties: % Solids 51.8; Particle size (nm)471; pH 5.0; Grits (200M) 0.013.

Latex M was formulated in SEMI-GLOSS PAINT SCREENING FORULATION I,except that no ethylene glycol was added, and tested for freeze thawstability.

The Latex M exhibited no coagulation after five cycles.

Example XII

All acrylic latex N was manufactured employing an anioniccopolymerizable surfactant, namely sodium salt of allyl ether sulfonate(Alcolac Ltd.), in place of the copolymerizable amphoteric surfactant ofExample X. The resultant latex had the following physical propeties: %Solids 52.6; particle size (nm) 533; grits (200M) 0.006. The latex N wasformulated in SEMI-GLOSS PAINT SCREENING FORMULATION I, having theamount of ethylene glycol noted below:

    ______________________________________                                                    Emulsion                                                                      L        M        N                                               ______________________________________                                        % Ethylene Glycol                                                                           0.sup.     0.sup.   3.sup.                                      Paint Properties:                                                             freeze-thaw   5.sup.a    5.sup.a  2.sup.b                                     (no of cycles)                                                                              (PASS)     (PASS)                                               ______________________________________                                         Notes:                                                                        .sup.a Remained liquid after 5 cycles                                         .sup.b Coagulated after 2 cycles                                         

Thus, the paints formulated with the amphoteric copolymerizablesurfactants of this invention exhibit superior freeze-thaw stability, ascompared with a paint formulation containing an anionic copolymerizablesurfactant and ethylene glycol.

Example XIII

An all acrylic latex, identified as O, was synthesized using cationiccopolymerizable surfactant namely methacrylamidopropyl-trimethylammonium chloride in place of the copolymerizable amphoteric surfactantof Example X. The following physical characteristics were obtained. %solids 49.5; particle size (nm) 302; pH 7.0; Viscosity (cps) 38; Grits(200M) 0.0013.

Latex was formulated in Semigloss Paint Formula II of Example III andtested for freeze-thaw stability. It coagulated during first cycle. Thusthe paints formulated with amphoteric copolymerizable surfactants ofthis invention exhibit superior freeze-thaw strength compared to thoseusing copolymerizable cationic surfactants.

Example XIV

Using the copolymerizable amphoteric surfactant monomer Hartomer HB-6380a styrene (St) latex identified as Latex P, was made. The followingmonomer and surfactant composition in pphm was used to make styreneacrylate copolymer.

    ______________________________________                                                       In PPHM                                                        ______________________________________                                        Styrene          15.0                                                         BA               53.5                                                         MMA              30.7                                                         Acryic Acid (AA) 1.0                                                          Hartomer HB-6380 2.2                                                          Rexol 25/40      0.6                                                          ______________________________________                                    

The resultant product had the following physical properties: % solids52.3; particle size (nm) 351; Viscosity (cps) 30.0.

Latex P was tested in Semigloss Paint Formula II of Example III whereinno ethylene glycol was present. The paint showed no sign of coagulationafter 5 freeze-thaw cycles.

Example XV

Using Hartomer HB-6380 monomer, a film forming all acrylic emulsion,(Identified as Latex Q) was produced. The following ingredientcompositions in pphm were used: BA 53; MMA 45.5; AA 1.0; HB-6380 2.2;Rexol 25/40 1.1. The following physical properties were observed: %solids 53.0; pH 7.0; particle size (nm) 351. The above resin wasformulated into Semigloss Paint Test Formula II of Example III whereinno ethylene glycol and no Texanol (coalescing solvent) was added tofurnish a solventless paint composition. The paint was tested forfreeze-thaw stability and scrub resistance. The following resultsresults were obtained:

    ______________________________________                                        Emulsion      Q           B                                                   ______________________________________                                        Surfactant    HB-6380     Siponate DS-10                                      F/T cycles    5 (Pass)    1 (Fail)                                            Scrubs        2552        1300                                                ______________________________________                                    

This example shows that solventless paint made with Latex Q showedsuperior freeze-thaw stability and scrub resistance (water resistance)as compared to the same paint made with Latex B using a conventionalsurfactant.

It is apparent that many modifications and variations of this inventionas hereinabove set forth may be made without departing from the spiritand scope thereof. The specific embodiments described are given by wayof example only and the invention is limited only by the terms of theappended claims.

What is claimed is:
 1. An improved latex for use in aqueous-based latexpaint formulations which comprises a latex copolymer, dispersed in waterin the presence of a surfactant wherein the improvement comprises usingas the surfactant about 1-4 pphm of an amphoteric surfactant of theformula ##STR5## wherein: R₁ =C₈ -C₂₀ alkylR₂ =H or C₁ -C₂ alkyln=1-4such that the latex paint formulation exhibits enhanced wetadhesion and freeze-thaw stability.
 2. The latex of claim 1, wherein thesurfactant further comprises about 1-3 pphm of a nonionic surfactant ofthe formula R--O--(CH₂ --CH₂ --O)_(n) --H wherein C₄ -C₁₂ alkylphenol orC₄ -C₁₈ alkyl and n is about 20-50.
 3. The latex of claim 1, wherein thelatex copolymer is an all acrylic latex copolymer.
 4. The latex paintformulation of claim 1, wherein the latex copolymer is a vinyl acryliclatex or a styrene acrylic latex copolymer.
 5. A latex paint formulationwhich comprises the latex of claim 1, an aqueous base, and, optionallyan organic antifreeze agent.
 6. The paint formulation of claim 5, whichcontains up to 2%, by wt, of an organic antifreeze agent.
 7. A methodfor improving the freeze-thaw stability and wet adhesion of a latexcopolymer for use within an aqueous based latex paint formulation thatcomprises preparing the latex copolymer in the presence of about 1-4pphm surfactant of the formula ##STR6## wherein R₁ =C₈ -C₂₀ alkyl; R₂ =Hor C₁ -C₂ alkyl; and n=1-4.